1. Field of the Invention
The invention relates in general to an ultrasonic lamp and a control method thereof, and more particularly to an ultrasonic lamp capable of preventing incorrect movement and a control method thereof.
2. Description of the Related Art
Having the feature of high frequency, the ultrasound has been widely used in many fields such as military, medicine and industries. However, with the advance in technology, the ultrasonic lamp has become one of the applications of the ultrasound technology. By continuously emitting a burst which hits a reflective object, the ultrasonic lamp can detect the time of flight of an echo, and then performs various controls according to the time length. However, if there are two or more than two ultrasonic lamps existing in the same space, errors might occur to the ultrasonic lamp due to the mutual interference of the echoes of the bursts emitted at similar frequencies.
Referring to FIG. 1, a timing diagram of the echo interference of two ultrasonic lamps L1 and L2 is shown. In FIG. 1, designations 110, 112 and 114 denote the bursts emitted by the ultrasonic lamp L1, and designations 120, 122 and 124 denote corresponding echoes of said bursts. Further, designations 130, 132 and 134 denote the bursts emitted by another ultrasonic lamp L2, and designations 140, 142 and 144 denote the corresponding echoes of said bursts. In general, the ultrasonic lamp determines the location of an object according to the first received echo reflected back from the object. Since the ultrasonic lamps L1 and L2 are located in the same space and the ultrasonic lamps L1 and L2 emit the bursts at different time points, the ultrasonic lamp L1 may receive the echo of the burst emitted by the ultrasonic lamp L2. For example, within a fixed period of time Δt after emitting the burst 110, the ultrasonic lamp L1 may receive the echo 140 of the burst 130 emitted by the lamp L2. Since the first received echo 140 is not the echo 120 that the lamp L1 is supposed to receive, the ultrasonic lamp L1 will make an erroneous determination to enter the control mode, hence incurring errors.